An LLC is used to hold business assets.A house-hack is a partial personal property / business property.You also have to separate business and personal assets within an LLC.So the question is would you be getting the protection that you are looking for by putting an asset that is partially personal within an LLC.You might also be losing your homestead exemption.Best of luck.

Question - I believe my personal umbrella policy should cover me personally assuming they cannot get me dismissed as an individual.

Since I am converting my Primary Residences into a STR MID-YEAR, does that go beyond the personal use days or does it start counting after STR service starts? 

I would do due diligence on this person - which due diligence is the #1 key in being successful in real estate

This home was built for an investor and next to a personal build I kept for myself.

But from my personal perspective their previous lease does not involve YOU at all.  

As a listing agent, I want buyers to see the property in person as much as humanly possible before we negotiate.

Work with a REALTOR with a solid marketing plan and a network of buyers. :)If you are trying to market specifically to investors, join local investor groups (in person or on facebook).

Hopefully you have a lease that you can point to that spells out things like "quiet enjoyment" and no unauthorized persons living at the property for more than 2 weeks, for example.

We've confirmed with the builder that they'll sell to investors if they go through my realtor, since they have a personal relationship.